Heaters are often used in the semiconductor device manufacturing, chemical processing, plastics manufacturing, commercial food processing, equipment manufacturing, and other manufacturing industries to heat or insulate piping, tubing, valve bodies, and other conduits having two-dimensional or three-dimensional curvature, particularly if processing or manufacturing requires that liquids or gases be transported at specific temperatures with limited heating or cooling or to prevent solidification of vaporous materials and consequent deposition of such materials on inside surfaces of the piping, tubing, valve bodies, and other conduits. The heaters can be thermally insulated from the ambient air to reduce the amount of power required and to minimize the outside temperature of the exposed heaters so that personnel who might contact them do not become accidentally burned.
For example, semiconductor manufacturing processes, such as Low Pressure Chemical Vapor Deposition (LPCVD) and aluminum etching, generate reaction byproducts, such as ammonium chloride gas (NH4Cl) or aluminum chloride (AlCl3) gas, in the effluent gas created in and discharged from the reaction process chamber. The ammonium chloride gas may solidify, deposit, and thereby cause a solid buildup on any cool surface, such as the inside surface of an unheated pipe conveying the gas to an exhaust or disposal site, vacuum pumps, and other equipment. This solid buildup in pipes, pumps, and other equipment downstream from the reaction process chamber can partially or even entirely plug the pipes, damage the pumps and other equipment, reduce vacuum conductance, and render piping, pumps, and other equipment used in the manufacturing process functionally impaired or inoperative.
The solid buildup caused by cooling can also flake apart and off the piping surfaces so as to become sources of contamination in the manufacturing process. A Low Pressure Chemical Vapor Deposition (LPCVD) process for depositing a coating of silicon nitride on substrate wafers used to form semiconductor chips, for example, creates this type of solid buildup by producing large amounts of ammonium chloride gas as a byproduct in the reaction chamber where the silicon nitride deposition occurs. Ammonium chloride gas typically sublimates at a temperature of less than one hundred degrees Celsius (100° C.) at 300 millitorr. Once the ammonium chloride gas leaves the reaction chamber and cools down, sublimation of the ammonium chloride causes a white crystalline material to form and build up on all unheated surfaces, such as on the insides of pipes and pumps used in the manufacturing system. The sublimated ammonium chloride can flake, break away, and flow back into the reaction chamber, where it can contaminate the semiconductor substrate wafers in the reaction chamber. If such contamination occurs, the manufacturing system must be shut down while the crystalline material is cleaned out of the system, and the clogged pipes and pumps have to be cleaned or replaced. In addition, the substrate wafers or semiconductor chips may have become so contaminated that they are worthless and beyond repair or use. In order to prevent the ammonium chloride gas from solidifying and clogging or contaminating the manufacturing system, heaters can be placed around the piping to preclude the ammonium chloride gas from cooling, sublimating, solidifying, or condensing until it reaches an area where it can be collected effectively and efficiently.
The use of heaters and other devices to heat and/or insulate objects, including pipes in the exemplary setting described above, is well-known in the art. For example, HPS Division of MKS Instruments, Inc., the assignee of the present invention, and Watlow Electric, Inc., developed a heater structure primarily for heating pipe components, valve bodies, and the like for the semiconductor processing industry. Their VacuComp™ Series 43 Valve Heater Jackets, Flexible Section Heater Jackets, Straight Section Heater Jackets, and Bend Section Heater Jackets are examples of these pipe component heaters, which use a thin fiberglass reinforced silicone heater mat laid flat and cut into flat patterns that, when pulled up and forced into three dimensional curves, will conform to the three-dimensional shapes of pipe components for which they are patterned. Flat sheets of silicone foam rubber are also cut into somewhat the same shaped, but smaller patterns and are then bonded to an exposed flat surface of the heater mats for heat insulation, leaving uncovered edge sections of the heater mat extending laterally outward from the silicone foam rubber insulation sheets. Lace hooks and laces are attached to the uncovered edge sections of the heater for pulling and fastening the pipe heater structures into curved, three dimensional configurations around the valve bodies, flexible, curved, and straight pipe sections, and other pipe components for which they are patterned.
U.S. Pat. No. 5,714,738, which is assigned to both the HPS Division of MKS Instruments, Inc., the assignee of the present invention, and Watlow Electric, Inc., shows a flexible insulated heater including a heater mat surrounded by an insulation jacket. The heater mat is preferably made of two layers of fiberglass reinforced rubber sheets laminated together with resistive heater wires sandwiched between the laminated sheets. The heater mat is formed with a curvature and sized to fit snugly around the peripheral surface of the pipe that is to be heated. A jacket of thermally insulating material, such as a polymer foam, is molded over the external surface of the heater mat. The insulated jacket holds the heat generated by the heater mat from escaping radially outward, and it protects against burns to persons who might touch the heater. The mat and the jacket are configured so that the heater has interfacing opposite edges and that meet and preferably touch each other when the heater is mounted on the pipe, but the combination of the mat and jacket have sufficient resilient flexibility to allow opening the heater by separating the edges enough to slip the heater over the pipe, whereupon the heater resumes its original inherent cylindrical shape when released. Snaps, Velcro™ fastening material straps, or other suitable fasteners can be used to secure the heaters snugly around the pipe, if desired, although the biased resilience of the heater to its formed shape is generally sufficient itself to hold the heater in place. A power cord, control cavity, and an optional overmold provide electric power to the heating wires or elements in the heating mat. A system of flexible insulated heaters can be daisy-chained or ganged together to heat and insulate a network of pipes. Exemplary embodiments of the heaters disclosed in U.S. Pat. No. 5,714,738 are sold by the Vacuum Products Groups of MKS Instruments, Inc. as Series 45 HPS™ heaters.
In semiconductor manufacturing, an ion beam implanter is used to alter the near surface properties of semiconductor materials. Solid or vapor source vessels are a method for the storage and safe delivery of arsine, phosphine, boron trifluoride, silicon tetrafluoride and germanium tetrafluoride for ion implantation. The solid or vapor source vessels allow gases to be delivered to the ion source region of an ion implanter with maximum gas vessel pressures of less than one atmosphere, eliminating the risks associated with the delivery of hazardous gases at higher pressures. The solid or vapor source vessel contains a solid material that absorbs a desired process gas and holds the gas at sub-atmospheric pressure levels. Previous methods for providing a source material include heating the material at high temperature in a crucible to produce a gas. The solid or vapor source vessels, however, are safer and provide a larger volume of useable material. SDS™ (Safe Delivery Source) brand vessels are an example of a solid or vapor source vessels.
In addition to providing heaters, MKS Instruments, Inc. also provides mass flow controllers. The Model M330 Mass Flow Controller (MFC), for example, has successfully been used with solid or vapor source vessels, such as the SDS™ brand vessels. The M330 was specifically designed to maintain the necessary flow control performance levels with an extremely low pressure drop across the MFC, allowing for more efficient use of solid source gas vessels. Phosphine, for example, can be effectively delivered at a rate of 0.8 sccm with an SDS™ gas vessel pressure as low as 1.5 Torr and 1 Torr at 0.5 sccm in an Acelis model GSD ion implanter. The low gas vessel operating pressures allow for a higher percent of the source gases to be used before refilling is necessary, reducing operating costs and increasing implanter system availability. The MKS M330 allows over 97% of the solid source vessel contents to be utilized for gas delivery.
What is further desired, however, are a new and improved system and method for heating solid or vapor source vessels and flow paths. Preferably, a new and improved system and method for providing stable and uniform heating of solid source vessels and flow paths that are substantially free of cold spots.